<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style>
			body {
				height: 1000px;
			}

			.container {
				float: left;
				border: 1px solid #000;
				display: flex;
				width: 290px;
				flex-wrap: wrap;
				justify-content: space-between;
				resize: both;
			}

			.list {
				width: 65px;
				height: 65px;
				margin-bottom: 10px;
				background-color: rgb(148, 148, 131);
				margin-right: 10px;
			}

			.list:nth-child(4n) {
				margin-right: 0px;
			}

			.container::after {
				content: '';
				display: block;
				flex: 1 1 auto;
			}
		</style>
	</head>
	<body>

		<div class="container">
			<div class="list"></div>
			<div class="list"></div>
			<div class="list"></div>
			<div class="list"></div>
			<div class="list"></div>
			<div class="list"></div>
			<div class="list"></div>
			<div class="list"></div>
			<div class="list"></div>
			<div class="list"></div>
			<div class="list"></div>
		</div>
		<div>
			切换子项目数量
			<select id="select">
				<option value="9">9</option>
				<option value="10">10</option>
				<option value="11">11</option>
				<option value="12">12</option>
				<option value="13">13</option>
				</selction>
		</div>


		<script>
			
			
			let container = document.querySelector('.container');
			let box = document.querySelector('#select')
			
			box.onchange = (e) => {
			  let len = e.target.value;
			  let html = Array.from({length: len}, () => `<div class="list"></div>`).reduce((pre, item) => {
			    return pre += item;
			  }, '');
			  container.innerHTML = html;
			}
			
			
		</script>
	</body>
</html>
